ML Wiki
Machine Learning Wiki - A collection of ML concepts, algorithms, and resources.

RDFS-Plus

semantic-web

RDFS-Plus

In Semantic Web RDFS-Plus is an extension of RDFS, and a subset of OWL

  • even though the namespace is OWL, it’s considered as a subset
  • Inference rules are shown with SPARQL CONSTRUCT queries
  • for logical semantics behind there expressions see Semantic Web Logic
  • DL-Lite something

Basic Constructs

owl:inverseOf: Inverse

Example

  • suppose we have :hasParent - then the inverse is :hasChild
  • the construction owl:inverseOf makes this relation explicit

In math,

  • inverse of $f$ is $f^{-1}$:
  • if $f(x) = y$, then $f^{-1}(y) = x$
  • the same idea is in RDFS-Plus
CONSTRUCT { ?y ?q ?x }
WHERE {
  ?p owl:inverseOf ?q .
  ?x ?p ?y .
}

Example:

  • lit:Shakespeare lit:wrote lit:Macbeth
  • we know that lit:wrote owl:inverseOf lit:writtenBy
  • so, can infer that lit:Macbeth lit:writtenBy lit:Shakespeare

owl:SymmetricProperty: Symmetric Properties

  • in real life, a relation “married” is both-way:
    • if $A$ is married on $B$, then $B$ is married on $A$
  • suppose we have this assertion: bio:Anne bio:married lit:Shakespeare
  • consider this query
    • SELECT ?who WHERE { ?lit:Shakespeare bio:married ?who }
    • it returns no answer
  • now state that married is both-way: it’s inverse of itself
  • bio:married owl:inverseOf bio:married
    • now that query returns something
  • this is an example of a owl:SymmetricProperty
    • so instead of owl:inverseOf can say
    • bio:married rdf:type owl:SymmetricType
CONSTRUCT { ?p owl:inverseOf ?p. } 
WHERE { ?p a owl:SymmetricProperty . }

Also, can be useful to say that owl:inverseOf is symmetric

  • owl:inverseOf rdf:type owl:SymmetricProperty
  • now the following hold:
    • $:P_1$ owl:inverseOf $:P_2 \Rightarrow$
    • $:P_2$ owl:inverseOf $:P_1$

owl:TransitiveProperty: Transitivity

In math:

  • $R$ is transitive if
  • $a \ R \ b \land b \ R \ c \Rightarrow a \ R \ c$

In RDFS-plus, owl:TransitiveProperty is used for that:

  • :P rdf:type owl:TransitiveProperty

Meaning:

CONSTRUCT { ?x ?p ?z .} 
WHERE {
  ?x ?p ?y . 
  ?y ?p ?x . 
  ?p a owl:TransitiveProperty . 
}

Note that for longer chains like $a \to b \to … \to q$ the rule also holds

owl:equivalentClass: Equivalence

Identity

  • URIs give the global notion of identity
  • but what if we merging two different sources that have the same concept, but under different URIs?
  • i.e. we want to say that $:A \equiv :B$
  • use RDFS:
    • :A rdfs:subClassOf :B $\land$ :B rdfs:subClassOf :A
  • semantically same effect is achieved with owl:equivalentClass
CONSTRUCT { ?r rdf:type ?b .} 
WHERE { 
  ?a owl:equivalentClass ?b . 
  ?r rdf:type ?a . 
}

CONSTRUCT { ?r rdf:type ?a .} 
WHERE { 
  ?a owl:equivalentClass ?b . 
  ?r rdf:type ?b . 
}

Note that we need to have 2 CONSTRUCT statements

  • because owl:equivalentClass is symmetric
  • but instead of repeating twice can say that
    • owl:equivalentClass rdf:type owl:SymmetricProperty
  • can add the following and have no need to state anything
    • owl:equivalentClass rdfs:subPropertyOf rdfs:subClassOf

owl:sameAs: Same Individuals

Suppose in 3 namespaces we have 3 different ways of describing a person

  • how we can say that in all these 3 cases something/somebody is the same resource?
  • e.g. pr:WilliamShakspere owl:sameAs lit:Shakespeare

it’s defined by 3 rules:

-- when it's a subject
CONSTRUCT { ?s ?p ?x. } 
WHERE {
  ?s ?p ?y.
  ?x owl:sameAs ?y .
}

-- when it's an object
CONSTRUCT { ?x ?p ?o. } 
WHERE {
  ?y ?p ?o .
  ?x owl:sameAs ?y .
}

-- when it's a predicate
CONSTRUCT {?s ?x ?o. } 
WHERE {
  ?s ?y ?o .
  ?x owl:sameAs ?y .
}

To avoid adding 3 more rules

  • say that it’s symmetric:
  • owl:sameAs rdf:type owl:SymmetricProperty

Sameness: Functional Properties

owl:FucntionalProperty

Functional - of functions (in math)

  • a property is functional if
  • for some input value there could be only one output value

Examples (from RL):

  • hasMother - can have only one biological mother
  • hasBirthplace
  • birthdate

In RDFS-plus use owl:FucntionalProperty to describe that

  • a property can give only one value for one particular entry 
    CONSTRUCT { ?a owl:sameAs ?b . } 
WHERE {
?p rdf:type owl:FunctionalProperty .
?x ?p ?a . 
?x ?p ?b . 
}

Note the semantics

  • if $x^2 = a \land x^2 = b \Rightarrow a = b$
  • so if some resources participate in a functional property
  • we conclude that these resources refer to the same entity (i.e. they are the same)

owl:InverseFunctionalProperty

Inverse of owl:FucntionalProperty

  • a single value of an inverse functional property cannot be shared by two entities
  • instead it infers that these two entities are the same
  • and it doesn’t signalize any errors
  • examples: SSN, driver license, etc - anything that can be an ID number 
    CONSTRUCT { ?a owl:sameAs ?b . } 
WHERE {
?p rdf:type owl:InverseFunctionalProperty .
?a ?p ?x . 
?b ?p ?x . 
}

Examples

Student ID

  • a student has an identity
  • this ID # belongs only to one person
  • so have this in the schema
    • :hasIdentityNo rdfs:domain :Student .
    • :hasIdentityNo rdfs:range xsd:Integer .
  • now ensure the uniqueness
    • :hasIdentityNo rdf:type owl:FunctionalProperty .
    • :hasIdentityNo rdf:type owl:InverseFunctionalProperty .

Summary

Functional Only

  • hasMotheris a functional property only.
  • Someone has exactly one mother, but many people can share the same mother.

Inverse Functional Only

  • hasDiary is an inverse functional property only
  • A person may have many diaries, but a diary is authored by one person only

Both Functional and Inverse Functional

  • SSN, Student #, etc

Other Constructs

owl:DatatypeProperty and owl:ObjectPropery

In RDF, subjects and objects are resource

  • they can be either another resources or some data items

Examples:

  • uni:studentId a owl:DatatypeProperty
  • bio:married a owl:ObjectProperty

owl:Class

owl:Class rdfs:subClassOf rdfs:Class .

See Also

Sources

✏️ Edit on GitHub